1. Field of the Invention
The present invention relates to a detachable optical module incorporated in an optical apparatus, such as an electrophotographic copier, and, more particularly, to a detachable optical module comprising a chassis on which various optical units are located, and which is detachably attached to a frame of the optical apparatus.
2. Description of the Related Art
As one type of optical module, an optical variable-magnification module for an electrophotographic copier is well known. This optical variable-magnification module comprises a rectangular chassis on which various optical units are located, and which is detachably attached to a frame of the electrophotographic copier. A movable mirror unit is known as a representative of the various optical units, and is provided on an upper surface of the chassis. Also, a movable focussing lens unit is known as another representative of the various optical units, and is provided on the upper surface of the chassis. Note, the movable focussing lens unit forms a part of an optical focussing system of the electrophotographic copier.
The movable mirror unit is operated in conjunction with the movable lens unit to vary a magnification of the optical focussing system of the electrophotographic copier. The movable mirror unit also serves to direct a light beam, passing through the movable focussing lens unit, to an area below the chassis of the optical module. To this end, the chassis has an opening formed therein, and the movable mirror unit is moved in the opening such that a lower portion of the movable mirror unit protrudes from the lower surface of the chassis, through the opening of the chassis.
In another type of optical module, an immovable mirror unit is provided in an opening of a chassis to direct a light beam from an upper side of the chassis to a lower side thereof, or vice versa. In this case, a lower portion of the immovable mirror unit protrudes from the lower surface of the chassis, through the opening thereof.
The optical module is independently manufactured and circulated. For example, the optical module is shipped to an optical apparatus manufacturer, such as an electrophotographic copier manufacturer, and is then incorporated into the optical apparatus as a preassembled unit. During shipping, the optical module is packed and protected.
Nevertheless, after the optical module is unpacked and is awaiting assembly in the optical apparatus, the optical module may be temporarily placed on a working table or a floor. In this case, the lower portion of the mirror unit, protruding from the lower surface of the chassis, may about against the working table or the floor, such that a detrimental force is exerted upon the mirror unit. When the lower portion of the mirror unit is subjected to the impact of placement, a positional readjustment of the mirror unit may occur or the mirror unit per se may be physically damaged.
Especially in regards to the optical variable magnification module for the electrophotographic copier, the movable mirror unit should be protected from impacts. This is because a positional relationship between the movable mirror unit and the movable focussing lens unit, in which the movable mirror unit is precisely extended perpendicularly to an optical axis of the movable focussing lens unit, has to be maintained before an image to be copied can be properly formed on a surface of a photosensitive drum.
In addition, in the electrophotographic copier having the optical variable-magnification module incorporated therein, while an object to be copied is illuminated with light emitted from a suitable light source, a part of the light emitted from the light source may, as stray light, become incident upon the movable mirror unit. Of course, when the stray light is directed to the photosensitive drum, the stray light appears as noise on a copied image.